Japanese Patent Publication (Kokoku) Nos. Sho 34-2041, Sho 41-13995, Sho 43-18800, and Sho 44-20116 describe high-molecular-weight organopolysiloxanes with viscosities varying in a wide range from a silicone oil to a silicone gum that can be obtained by subjecting a low-molecular-weight cyclic organosiloxane to emulsification dispersion, and ring-opening polymerization in the presence of a surface-active agent and a polymerization catalyst.
Normally, the aforementioned low-molecular-weight organosiloxanes required for emulsion polymerization are used in the form of a cyclic organosiloxane oligomer such as octamethylcyclotetrasiloxane which is readily available and can be easily emulsified and polymerized by ring-opening. However, because ring-opening polymerization of the cyclic organosiloxane oligomer is an equilibrium reaction, upon completion of emulsion polymerization, the polyorganosiloxane normally contains the cyclic organosiloxane oligomers, such as octamethylcyclotetrasiloxane, in an amount of 8 to 15 wt. %. Furthermore, the obtained emulsion system has low physical stability because of the volatile nature of the obtained oligomers. When hair-care cosmetic materials dispersed in aforementioned emulsions are used in large amounts, e.g., in such places as beauty salons, especially when the hair-care product is used for heat-blow treatment of hair, the cyclic organosiloxane oligomer evaporated from the emulsion may contaminate the environment either by polluting the ventilation system, or by damaging contacts of fan heaters or various other electrical appliances.
Furthermore, when the aforementioned emulsion is used in conjunction with skin-care products, volatility of the siloxane oligomer may lead to undesired contact of the oligomer with the skin.
Therefore, when a polyorganosiloxane emulsion is used for preparation of cosmetic products, it may be required to limit the amount of cyclic organosiloxane oligomers used in the emulsion. However, it is difficult to selectively delete only residual cyclic organosiloxane that remains after the emulsion polymerization, without deteriorating the polyorganosiloxane emulsion.
Japanese Patent Publication (Kokoku) No. Sho 41-13995, Japanese Patent Application Publication (Kokai) Nos. Sho 63-265924 and Hei 4-178429 disclose a process, in which a polydiorganosiloxane having molecular ends capped with silanol groups is emulsified in water in the presence of a sulfonic acid catalyst that possesses a surface-active action such as a benzenesulfonic acid substituted with an aliphatic hydrocarbon group, in a high-pressure homogenizer. Upon completion of emulsification, the emulsion is retained at room temperature and is polymerized. A substance, which is normally used in emulsion polymerization as a catalyst that also functions as a surface-active agent, is an easy emulsifiable and readily available dodecylbenzenesulfonic acid, or a similar alkylbenzenesulfonic acid.
However, when an alkylbenzenesulfonic acid is used, even though it is neutralized after polymerization, salts thereof remain in the emulsion, and when the emulsion is in use, these salts change color under the effect of ultraviolet rays.
Furthermore, the use of alkylbenzenesulfonic acids is undesirable from the environmental point of view because of their low biodegradation. alkylbenzenesulfonic acid salts possess high detergency. Therefore, when a polyorganosiloxane emulsion prepared with an alkylbenzenesulfonic acid is used as a raw material for cosmetic products, an excessive amount of these salts irritates skin of the body, skin of the head, and hair. This not only decreases the effect of the cosmetic products, but also may cause irritation of the skin, appearance of dandruff on the head skin, and damage the hair.
Based on the study aimed at the solution of the aforementioned problems, the inventors arrived at the present invention. More specifically, it is an object of the present invention to provide a stable polyorganosiloxane emulsion composition that possesses excellent cosmetic functions required for dampness and smoothness. Another object is to provide a cosmetic raw material prepared from the aforementioned emulsion composition.